1. Field of the Invention
The present invention relates generally to seatbelt restraint systems for vehicles and, more particularly, to a seatbelt pretensioner for a seatbelt restraint system in a vehicle.
2. Background
Seatbelt restraint systems for restraining an occupant in a vehicle seat play an important role in vehicle crash situations. Seat restraint systems commonly have a lap belt section and a shoulder belt section. In general, the lap belt section and the shoulder belt section are connected together at one end. A seat restraint system includes a buckle at the connected end. The seat restraint system also includes a latch plate connected at one end by webbing that is attached to the vehicle structure and/or the seat. The buckle receives the latch plate to be buckled together. When the buckle and the latch plate are buckled together, the seat restraint system restrains movement of the occupant during a collision.
OEM vehicle manufacturers often incorporate pretensioning devices, which tension the seatbelt prior to full impact of a vehicle, to enhance restraining the occupant to the seat. One type of pretensioning device is a pyrotechnic lap pretensioner (PLP). Various designs are known, including a type of PLP which uses a cable to connect a piston at one end to seatbelt webbing at the other end. When a collision occurs, a pyrotechnic charge is fired, producing gas which pressurizes a gas chamber within a tube, to force the piston down the tube. Since the seatbelt webbing is ultimately connected to the piston via the cable, the seatbelt moves in conjunction with the piston, tightening the belt around the occupant.
This design, however, has several shortcomings. One problem is that the cable is connected to the piston at a portion of the piston that is closest to the pyrotechnic charge or gas generator. The corresponding portion of the tube where this connection occurs is within the gas chamber and accordingly, the cable runs through the gas chamber. An aperture, which opens into the gas chamber, is formed by the tube for the cable. This makes it difficult to seal the gas chamber so consequently, some of the gas and therefore energy produced by the charge is lost through the aperture.
Another problem with current designs of PLP's is that OEM's and many end users consider the cable connection between the seatbelt webbing and the PLP visually objectionable. Accordingly, often times a cover piece is placed over and connected directly to the cable. The cover piece is typically a styled, grained and molded-in-color plastic trim part. When a charge is fired, the cable moves which correspondingly moves the cover piece. However, the cover piece can sometimes interfere with tensioning of a seatbelt, because the cover piece may interact with a stationary, decorative trim disposed about the seat.
Moreover, the cover piece serves merely an aesthetic function and provides minimal to no pretensioning function. Accordingly, an alternative design which eliminates the cable, the cover piece and preferably does not diminish the visual appearance of the PLP-webbing connection is desirable.